International Review of Hydrobiology最新文献

The goal of this study is to experimentally assess the possible effect of macroinvertebrate predators on the decomposition rate of leaves in a Mediterranean stream and to analyze the pattern of colonization by macroinvertebrates of the litter bags through time. We designed a factorial experiment with three types of litter bags (allowing the entrance of no macroinvertebrates, only small macroinvertebrates and small and large, top-predators, macroinvertebrates). We measured the percentage of ash-free dry mass remaining after 15, 30, and 45 days, as well as the macroinvertebrate community composition of the two types of litter bags where they were allowed to enter. We did not find differences in the ash-free dry mass remaining between the two types that allowed the entrance of macroinvertebrates. The diversity of the community colonizing each type of litter bag was always relatively high and changed significantly with time and, in some cases, with the exclosure treatment studied. These results show the absence of important top-down control of macroinvertebrates and particularly in those involved in the leaf decomposition in the food web of this Mediterranean stream that could have repercussions on the leaf decomposition process.

Stratification dynamics in reservoirs have a great impact on ecosystem functioning and biogeochemical cycling, and can be strongly influenced by wind events. In this study, a well-established one-dimensional hydrodynamic model (GLM) was used to investigate the response of stratification dynamics in Rappbode Reservoir to different wind conditions, in particular to episodic strong wind events. In years with increased wind speed, stratification duration and intensity were reduced. Episodic wind forcing by strong wind events are important determinants of thermal structure and can induce persisting shifts in the thermal structure that remain over the season until the next overturn. The results showed that reductions in stratification intensity were particularly distinct when the strong wind occurred in early summer. Strong wind events outside of this sensitive time window did not exert an important impact on the thermal dynamics of the reservoir. Our research confirms the decisive impact of wind speed on stratification of lakes and reservoirs. It effectively illustrates the sensitive time window of thermal dynamics to episodic wind events.

To clarify the effect of brownification on the functioning of lake ecosystems, the utilization of daytime refuges by chaoborids was examined in two lakes having different water color. It was hypothesized that with high water color, oxygen concentration plays a smaller role for the behavior of chaoborids than with lower water color. It was also expected that the depth distribution of chaoborids is associated with light intensity at 680–700 nm. This could decrease their visibility to predators. In Lake Iso Valkjärvi with 50 mg L⁻¹ Pt water color, chaoborids occurred below 5 m depth, where the oxygen concentration was 0.4 mg L⁻¹. Supporting the first hypothesis, in Lake Majajärvi with 340 mg L⁻¹ Pt color, the leading edge of the population was at 3 m with 3.5 mg L⁻¹ oxygen concentration. In Majajärvi, chaoborids remained in a layer where planktivorous fish could feed, explained by the low light intensity that decreased the potential predation pressure of fish. In Iso Valkjärvi with higher light intensity, chaoborids inhabited only the layers where oxygen concentration was too low for fish. Supporting the second hypothesis, the intensity of 693 nm light in the two lakes was similar at the depth of the leading edge of the chaoborid population. This wavelength represents the wavelengths that chaoborids reflect most effectively and is beyond the sensitivity peak of their main predator perch. The results suggested that combined effects of oxygen and water color are potential explanatory mechanisms of the observed patterns in the behavior of chaoborids. The results thus suggested that along the worldwide brownification of lakes, the role of oxygen as a regulator of invertebrate predators may change. Because invertebrate predators are important components of lake food webs, such effects may be reflected to the whole ecosystem and further studies on the subject are encouraged.

Allelopathic picocyanobacteria have been responsible for harmful incidents with severe ecological impacts in many parts of the world. The allelopathic interactions that have been shown to be implied in the dominance of various species of phytoplankton, forming massive blooms, are influenced by environmental factors such as nutrient concentration. This study aims to determine in what extent the allelopathic activity of the bloom-forming picocyanobacterium Synechococcus sp. is impacted by water stoichiometry. We measured the allelopathic activity of Synechococcus sp. on growth, chlorophyll fluorescence, and photosynthetic performance of green algae Chlorella vulgaris and Oocystis submarina and diatoms Bacillaria paxillifer and Skeletonema marinoi by addition of cell-free filtrate obtained from cultures growing in nutrient-sufficient (NP), nitrogen-deficient (−N), or phosphorus-deficient (−P) culture medium. These studies indicated that sufficient amounts of nutrients affected the picocyanobacterium increasing its production of allelochemicals. Conversely, the weakest allelopathic activity was recorded after the addition of a filtrate obtained from Synechococcus sp. grown at −N medium. The highest decline in growth, the maximum quantum yield of photosystem II (PSII) photochemistry (F_v/F_m) and the photosynthetic capacity (P_m) were observed for diatom S. marinoi. On the other hand, Synechococcus sp. filtrate had no allelopathic effects on O. submarina. While confirming the allelopathic activity of Synechococcus sp. these findings show that production of allelopathic substances is influenced by the availability of nutrients.

Anthropogenic translocations are the main vectors of intercontinental invasions. Molecular tools have been important in the study of biological invasions, helping to identify the source of non-native species mainly when these species are rapidly colonizing the new territories. The aims of this study were: (i) to characterize genetic sequences of the Daphnia lumholtzi population in Brazil (Upper Paraná River floodplain) for the first time; (ii) to compare these sequences with available sequences at GenBank; and (iii) to contribute new sequences of gene 12S from D. lumholtzi. Specimens were collected from a lake of the Paraná River for gene comparison (COI and 12S sequences). Genetic sequences from populations outside Brazil were obtained from GenBank. D. lumholtzi specimens sequenced in this study are genetically close to populations from the United States and Mexico and considerably distant from Australian populations. Our data confirm that populations present in the Paraná River floodplain probably came from the United States, where they arrived through introduction of African fish. The genetic similarity between our specimens and populations from Mexico and the morphological discrepancy between them reinforces the importance of molecular analysis for accurate identification of a species and its origin.

This study assessed the genetic relationship between Evadne nordmanni of the Baltic Sea and the North Sea from sequence variation of the mitochondrial cytochrome c oxidase subunit I gene (COI) of 88 specimens from 13 different sites, and from further published data from the Atlantic and Pacific basins. The COI sequences of E. nordmanni from the North and Baltic Seas were represented by a coherent cluster of 28 haplotypes dominated by a central haplotype that accounted for over half of the individuals from these seas, from all samples except one from the Arkona Basin (Baltic Sea). Overall, the North and Baltic Sea populations appear relatively homogenous and the North Sea plausibly represents the source population for the Baltic one. However, the haplotype network also involved a haplogroup of exclusively Baltic Sea haplotypes, comprising four haplotypes represented by 21 individuals and strongly dominated by specimens from the Arkona basin. This inspires discussion about the post-glacial evolution of a genetically distinct Baltic Sea group, related to a special local salinity regime. Partly as a reflection of the presence of the unique haplogroup, the mean haplotype diversity in the Baltic was twice as high as the mean diversity in the North Sea, h = 0.64 versus h = 0.30.

Due to their competitive advantage when inorganic nitrogen (N) sources are scarce, it is widely assumed that the abundance and N₂-fixation rate of N₂-fixing cyanobacteria (Nostocales) would increase in response to reduced N loading. If realized, this response would render efforts to improve water quality by N reduction ineffective. To assess this, we performed a microcosm experiment using water from an N limited lake, Langer See, in which phosphorus loading was held constant, while a gradient of decreasing N loading was simulated. Nostocales biovolume increased over time in all microcosms, regardless of the N addition rate, so that no difference in Nostocales biovolume developed between high and low N microcosms. In contrast, the biovolumes of other taxa (especially non-fixing cyanobacteria) were lower at low N addition rates. N₂-fixation increased in low N microcosms, compensating for 36% of the difference in N addition by day 6. However, this compensation rate was achieved at Nostocales biovolumes far higher than those typical in the studied lake. At biovolumes typical for summer the compensation rate would only account for 7% of the omitted N. If these results were to hold over longer time scales, in shallow polymictic lakes like Langer See, reduced N loading may lower both in-lake N concentrations and biovolumes of non-fixing phytoplankton without significantly impacting Nostocales biovolume.

Excretion of nutrients by zooplankton is a complex process crucial for the functioning of aquatic ecosystems. Most of the available literature data concern excretion in freshwater or marine ecosystems, but little is known about the nutrients regeneration in brackish water bodies, and the described research results are often inconclusive. Therefore, the aim of this study was to investigate the intravital release of nitrogen and phosphorous in brackish water bodies and to analyze the effect of salinity levels on the process of excretion. Studies on excretion were based on laboratory experiments. In 2010, the rate of intravital release of nutrients by zooplankton sampled from the natural environment of the Vistula Lagoon and Lake Łebsko was analyzed in order to estimate the rate of excretion of nitrogen and phosphorus depending on the salinity level. A similar experiment was also carried out on monocultures of Brachionus calyciflorus. Results from studies on natural populations revealed variable rates of nutrients excretion for different levels of salinity. This correlation, however, was not statistically significant. Experiments on B. calyciflorus monocultures showed a significant (p < 0.05) linear correlation between salinity and excretion. The study demonstrated that higher concentrations of salts dissolved in water accelerate the rate of nutrients regeneration by zooplankton. The investigated process is determined by many factors, and for the reliable estimation of the excretion rate a multivariate analysis should be performed.